In recent years, soft silicone hydrogel contact lenses become more and more popular because of their high oxygen permeability and comfort. “Soft” contact lenses can conform closely to the shape of the eye, so oxygen cannot easily circumvent the lens. Soft contact lenses must allow oxygen from the surrounding air (i.e., oxygen) to reach the cornea because the cornea does not receive oxygen from the blood supply like other tissue. If sufficient oxygen does not reach the cornea, corneal swelling occurs. Extended periods of oxygen deprivation cause the undesirable growth of blood vessels in the cornea. By having high oxygen permeability, a silicone hydrogel contact lens allows sufficient oxygen permeate through the lens to the cornea and to have minimal adverse effects on corneal health.
One of lens forming materials widely used in making silicone hydrogel contact lenses is polymerizable polysiloxane. The main function of the polymerizable polysiloxane is to provide high oxygen permeability to resultant contact lenses. However, because of its hydrophobic nature, a polymerizable polysiloxane is generally not compatible with hydrophilic components in a lens formulation, including, e.g., hydroxyethylmethacrylate, hydroxyethylacrylate, N,N-dimethylacrylamide, N-vinylpyrrolidone, or an internal wetting agent. It would be difficult to obtain homogeneous lens formulations.
Therefore, there is a need for new actinically-polymerizable polysiloxanes suitable for making silicone hydrogel contact lenses.